Laboratory studies of a new adjuvant developed by BioSante Pharmaceuticals suggest that it could be used to make limited supplies of vaccine against the H5N1 strain of bird flu stretch further should a pandemic occur.

BioSante said that preclinical studies of BioVant (calcium phosphate nanoparticle adjuvant) showed that it could boost the immune response of mice exposed to the H5N1 viral antigen, stimulating the production of more antibodies than the antigen alone.

Attempts by the US Government to stockpile supplies of H5N1 antigen for use in mass vaccination programmes suffered a setback last month after a clinical trial of Sanofi Pasteur’s candidate found that it only worked at the highest dose tested.

The USA has already spent $150 million purchasing the vaccine, and had hoped to have enough to immunize at least 20 million people. But the trial suggested current stocks would only provide enough doses for 4 million, while the effectiveness rate even at the high dose was only around 54%.

BioSante suggested that its adjuvant could potentially be used to hike the effectiveness of the vaccine and allow it to be delivered with a lower dose of antigen, without the side effects associated with alum, the most widely-used adjuvant at present.

Steve Bell, vice president of research and preclinical development at BioSante, will present the avian flu data on May 8 at the Ninth Annual Conference on Vaccine Research in Baltimore.

Meanwhile, other companies developing vaccines against the H5N1 strain of avian flu are already looking at using adjuvants in the formulation, For example, GlaxoSmithline has started human trials of two versions of its candidate, one using alum and a second using a novel adjuvant. Results from these studies are due in the third quarter of this year.